Alkaline phenol-formaldehyde aqueous-based binders are used to bind fiberglass fibers together to generate a tightly bound system after thermal curing. Alkaline phenol-formaldehyde binders may also contain an excess of formaldehyde and these systems are typically extended by using relatively inexpensive urea that is incorporated in the cured resin. The degree of polymerization of these resins is sufficiently advanced to provide appropriate viscosity and cure profiles. These binder solutions and relatively short segments of narrow diameter glass fibers are typically co-deposited on a continuous conveyor belt with the aid of a vacuum that is drawn through the mat. These type resins are typically cured within 1-1.5 minutes at about 400° F. within air-blown ovens where evaporation of water occurs initially and the resin is at about 400° F. for only about 20 seconds. Under these conditions, evaporation of water initially occurs and this is followed by curing of the phenol formaldehyde binder to a crosslinked state. These binder solutions tend to accumulate at the glass fiber touching points within the fiberglass matrix which leads to effective binding of glass fibers to each other at these points to generate a tightly bound three dimensional system. Relatively low initial resin viscosities coupled with production of a rigid cured resin are desired since these properties allow expansion of the fiberglass matrix when the cured fiberglass mat exits the curing oven in a compressed state. Attaining a high degree of expansion after the cured mat exits the oven is important in achieving a highly insulating material as measured by relatively high R values. Also, a rigidly bound system will allow compression for packaging and shipping and expansion to nearly the original dimensions after removal from the shipping wrapping.
Fiberglass mats prepared from phenol-formaldehyde or phenol-urea-formaldehyde resins are typically used for insulation and molded media and structural board in residential and commercial applications. Use of these materials in these environments can cause significant health effects since the materials are known to slowly release formaldehyde that is a known toxic substance. Hence, many alternate binder resin compositions have been proposed and (or) are in use that do not incorporate formaldehyde. It is also highly desirable that any replacement resin be water-borne to avoid solvent emissions during manufacturing.
Many of these replacement resins are aqueous compositions of polymeric carboxylic acids and polyols that undergo thermal curing by esterification of the polymeric carboxylic acid with the polyol to generate a three dimensional crosslinked polyester system. U.S. Pat. Nos. 5,318,990 and 5,763,524 describe aqueous solutions of polymeric carboxylic acids such as polyacrylic acid (PAA) that are esterified with trihydric polyols such as glycerin (glycerol) or trimethylolpropane while using a salt of a phosphorous containing acid such as sodium hypophosphite as a catalyst. U.S. Pat. No. 6,274,661 describes an aqueous solution of a polymeric carboxylic acid, a trihydric alcohol, a salt of phosphorous containing acid, and various corrosion inhibitors. In the systems described above, a corrosion inhibitor is desirable since the binder solutions are generally acidic which can cause erosion of carbon steel components of the thermal curing system. A variety of other binder compositions containing polymeric carboxylic acids and polyols are described in U.S. Pat. Nos. 6,221,973; 6,699,945; 6,734,2237; 6,818,694; 6,884,838; and 6,884,849. Binder compositions containing polymeric carboxylic acids and activated polyols such as beta-hydroxyethylamides are described in U.S. Pat. Nos. 5,143,582; 5,340,868 and 6,221,973.
Whereas these polyester binders prepared from the esterification of polymeric carboxylic acids and polyols do not liberate formaldehyde during curing or use, major deficiencies still exist in polyester binders. One is that their curing times are relatively long; leading to decreased production rates of cured fiberglass mats. Decreased production rates require larger or increased number of production lines to produce the required amount of cured fiberglass mat, typically resulting in increased capital and plant operating costs. Another deficiency of polyester binders is the relatively low pH (corresponding to relatively high acidities) of these systems caused by the required high concentrations of carboxylic acid functionality. Low binder pH can cause significant erosion of binder curing equipment and facilities unless this equipment is composed of high quality steel to prevent corrosion. Another deficiency of cured polyester binders is their relatively high flammability since they are produced from combustible aliphatic polymeric carboxylic acids and polyols.